The use of tertiary amines in the production of polyurethane systems is known. A multitude of structurally different amines are used here as catalysts. Polyurethane systems are, for example, polyurethane coatings, polyurethane adhesives, polyurethane sealants, polyurethane elastomers or polyurethane foams, also referred to as PU foams.
Particularly in the case of production of polyurethane foams, tertiary amines play an important role, since what is called the blow reaction—water reacts with isocyanate to form carbon dioxide as blowing gas—and the gel reaction—polyols react with isocyanates to give urethanes, which leads to a rise in the molar mass and corresponding gelation—have to be matched exactly to one another here, in order that a high-quality foam can form.
Polyurethane foams are cellular and/or microcellular polyurethane materials and can be divided roughly into closed-cell or partly closed-cell rigid polyurethane foams and open-cell or partly open-cell flexible polyurethane foams. Rigid polyurethane foams are used predominantly as insulation materials, for example in refrigerator systems or in the thermal insulation of buildings. Flexible polyurethane foams are used in a multitude of technical applications in industry and the domestic sector, for example for sound deadening, for production of mattresses or for cushioning of furniture. A particularly important market for various types of PU foams, such as conventional flexible foams based on ether or ester polyols, cold-cure flexible foams, also referred to as cold-cure foams hereinafter (frequently also as “high-resilience” (HR) foams), and rigid foams, and also foams having properties between these classifications, is the automobile industry. It is possible here, for example, to use rigid foams as inner roof liner, ester foams as interior door trim and for die-cut sun visors, and cold-cure and flexible foams for seat systems.
Flexible foams may also be subdivided into cold-cure flexible foams and hot-cure flexible foams, as described for example in EP 2042534 A1, fully incorporated herein by reference.
A challenge in the provision of polyurethane systems and especially the polyurethane foams is that of product emissions. These should ideally be as low as possible.
In particular, there has been a constant increase in the last few years in the severity of the demands made by automobile manufacturers on their foam suppliers and the demands made by the mattress and furniture upholstery industry with regard to the emission specifications of polyurethane systems. Subjects of analytical determination in this context include the fogging characteristics (fogging means the precipitation of fog on the windscreen resulting from condensation of volatile constituents that condense readily at room temperature) of materials in automobile interiors, in order to increase driving safety, and the content of volatile organic compounds (VOCs) in these materials resulting from thermal desorption, summarized, for example, in the analysis method according to test methods VDA 278 of the German Association of the Automotive Industry, last updated in October 2011. Methods at room temperature may also be of significance for the classification, for example test chamber methods according to DIN Standard DIN EN ISO 16000-9:2008-04, which are of particular relevance for applications in the mattress and furniture upholstery sector. As well as the quantitative determination of the total emissions (VOC and fogging), some methods also require the attribution of the emissions to individual chemical compounds. For instance, pollutant tests in independent testing and certification systems, for example for textile raw materials, intermediates and end products at all processing stages in the context of the Öko-Tex Standard 100, focus on amines too as potential pollutants. The specified limits for attaining such certificates are often reflected in the demands on the foam specifications in the production of polyurethane foams, especially when the foams are being produced for the automobile, furniture upholstery or mattress industry. The constantly increasing severity of classifications and limits for amines is requiring, according to the application and demand, a constant adjustment of the formulations and in some cases even substitution of established nitrogen compounds, especially of amine catalysts, for new technologies.
A particular challenge in polyurethane foam production is that the use of emission-optimized amine catalysts should not cause any disadvantages in the foaming operation and with regard to the properties of the finished polyurethane system. In this connection, particular attention is paid to the activity of the catalysts. It is well known that emission-optimized amine catalysts generally have lesser catalytic activity than conventional non-reactive amine catalysts. This is because amines of high molecular weight or amines bearing isocyanate-reactive groups, called reactive amines, are generally used here. Amines of high molecular weight are no longer volatile because of the high molar mass, are less readily emitted from the foam and have a lower molecular mobility, but this also reduces catalytic activity. Reactive amines are incorporated into the PU matrix through reaction via their functional groups, usually OH or NH groups, thus hindering the mobility thereof and leading to lower amine emissions. In both cases, amounts of amine catalysts used are in some cases considerably greater than for established non-reactive amine catalysts. Moreover, even some established reactive amine catalysts no longer meet the demands of the emission tests (e.g. VDA 278) because of the increasing severity of the limits as described above.
A further difficulty, particularly in connection with the use of reactive amines, is also what is called recatalysis. As a result of the reduction in the activation barrier, catalysts accelerate not just the forward reaction but also the reverse reaction. Foams which have been produced with reactive amines thus often exhibit distinctly worsened ageing characteristics, for example in the humid ageing test or in the case of dry heat ageing.
A further difficulty is that reactive amine catalysts in particular can lead to troublesome odor nuisance in foam production, but also in relation to the finished foam.
There is therefore quite generally a constant need for further catalysts, preferably nitrogenous catalysts, especially amines or amine mixtures, which have good processibility and high catalytic activity, are safely handled and are suitable for production of polyurethanes and polyurethane foams having low emission or at worst associated with minor emissions, preferably suitable for production of low-odor polyurethane systems, without any adverse effect on important foam properties such as foam hardness or ageing characteristics.
Against this background, the specific problem to be solved by the present invention was that of providing polyurethanes having low amine emissions or at worst associated with minor amine emissions, especially polyurethane foams, preferably flexible polyurethane foams, preferably having low odor.